/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */

/*
 * This package is based on the work done by Timothy Gerard Endres
 * (time@ice.com) to whom the Ant project is very grateful for his great code.
 */

package org.apache.tools.tar;

/**
 * This class provides static utility methods to work with byte streams.
 */
public class TarUtils{

    /**
     * Parse an octal string from a header buffer. This is used for the file permission mode value.
     * 
     * @param header
     *            The header buffer from which to parse.
     * @param offset
     *            The offset into the buffer from which to parse.
     * @param length
     *            The number of header bytes to parse.
     * @return The long value of the octal string.
     */
    public static long parseOctal(byte[] header, int offset, int length){
        long result = 0;
        boolean stillPadding = true;
        int end = offset + length;

        for(int i = offset; i < end; ++i){
            if(header[i] == 0){
                break;
            }

            if(header[i] == (byte)' ' || header[i] == '0'){
                if(stillPadding){
                    continue;
                }

                if(header[i] == (byte)' '){
                    break;
                }
            }

            stillPadding = false;
            result = (result << 3) + (header[i] - '0');
        }

        return result;
    }

    /**
     * Parse an entry name from a header buffer.
     * 
     * @param header
     *            The header buffer from which to parse.
     * @param offset
     *            The offset into the buffer from which to parse.
     * @param length
     *            The number of header bytes to parse.
     * @return The header's entry name.
     */
    public static StringBuffer parseName(byte[] header, int offset, int length){
        StringBuffer result = new StringBuffer(length);
        int end = offset + length;

        for(int i = offset; i < end; ++i){
            if(header[i] == 0){
                break;
            }

            result.append((char)header[i]);
        }

        return result;
    }

    /**
     * Determine the number of bytes in an entry name.
     * 
     * @param name
     *            The header name from which to parse.
     * @param buf
     *            The buffer from which to parse.
     * @param offset
     *            The offset into the buffer from which to parse.
     * @param length
     *            The number of header bytes to parse.
     * @return The number of bytes in a header's entry name.
     */
    public static int getNameBytes(StringBuffer name, byte[] buf, int offset,
        int length){
        int i;

        for(i = 0; i < length && i < name.length(); ++i){
            buf[offset + i] = (byte)name.charAt(i);
        }

        for(; i < length; ++i){
            buf[offset + i] = 0;
        }

        return offset + length;
    }

    /**
     * Parse an octal integer from a header buffer.
     * 
     * @param value
     *            The header value
     * @param buf
     *            The buffer from which to parse.
     * @param offset
     *            The offset into the buffer from which to parse.
     * @param length
     *            The number of header bytes to parse.
     * @return The integer value of the octal bytes.
     */
    public static int getOctalBytes(long value, byte[] buf, int offset,
        int length){
        int idx = length - 1;

        buf[offset + idx] = 0;
        --idx;
        buf[offset + idx] = (byte)' ';
        --idx;

        if(value == 0){
            buf[offset + idx] = (byte)'0';
            --idx;
        }else{
            for(long val = value; idx >= 0 && val > 0; --idx){
                buf[offset + idx] = (byte)((byte)'0' + (byte)(val & 7));
                val = val >> 3;
            }
        }

        for(; idx >= 0; --idx){
            buf[offset + idx] = (byte)' ';
        }

        return offset + length;
    }

    /**
     * Parse an octal long integer from a header buffer.
     * 
     * @param value
     *            The header value
     * @param buf
     *            The buffer from which to parse.
     * @param offset
     *            The offset into the buffer from which to parse.
     * @param length
     *            The number of header bytes to parse.
     * @return The long value of the octal bytes.
     */
    public static int getLongOctalBytes(long value, byte[] buf, int offset,
        int length){
        byte[] temp = new byte[length + 1];

        getOctalBytes(value, temp, 0, length + 1);
        System.arraycopy(temp, 0, buf, offset, length);

        return offset + length;
    }

    /**
     * Parse the checksum octal integer from a header buffer.
     * 
     * @param value
     *            The header value
     * @param buf
     *            The buffer from which to parse.
     * @param offset
     *            The offset into the buffer from which to parse.
     * @param length
     *            The number of header bytes to parse.
     * @return The integer value of the entry's checksum.
     */
    public static int getCheckSumOctalBytes(long value, byte[] buf, int offset,
        int length){
        getOctalBytes(value, buf, offset, length);

        buf[offset + length - 1] = (byte)' ';
        buf[offset + length - 2] = 0;

        return offset + length;
    }

    /**
     * Compute the checksum of a tar entry header.
     * 
     * @param buf
     *            The tar entry's header buffer.
     * @return The computed checksum.
     */
    public static long computeCheckSum(byte[] buf){
        long sum = 0;

        for(int i = 0; i < buf.length; ++i){
            sum += 255 & buf[i];
        }

        return sum;
    }
}
